Methods and apparatus for separating solids having different specific gravities



Dec. 25, 1956 Fileck July 29. 1953 FIG 1 3 Sheets-Sheet l Dec. 25, 1956 K. F. TROMP 2,775,346

METHODS AND APPARATUS FOR SEPARATING SOLIDS HAVING DIFFERENT SPECIFIC GRAVITIES Filed July 29. 1953 3 Sheets-Sheet 2 FIGZ Dec. 25, 1956 K. F. TROMP 2,775,346

METHODS AND APPARATUS FOR SEPARATING SOLIDS HAVING DIFFERENT SPECIFIC GRAVITIES Filed July 29. 1953 3 Sheets-Sheet. 5

3 ii I as y I a g 23 30 K United States Patent 2,775,346 METHODS AND APPARATUS FOR SEP r- ING SOLIDS HAVING DIFFERENT SPECIFIC GRAVITIES p Klaas FiTromp, Bilthoven, Netherlands Application July 29, 1953, Serial No. 371,105 Claims priority, application France August 6, 1952 Q SClaims. (Cl. 209-4725) This invention relates to methods and apparatus for separating solids having different speciiicgravities in a tank containing a suspension whose density increases in a direction from the level of the suspension to the bottom of the tank, wherein the middlings, i. e. the suspended solid products, isolated from the floating andthe sinking products, are carried, by means of substantially horizontal, rectilinear currents produced at various heights inthe bath, towards outlet openings of the. tank, through which they are discharged together with said currents run-ofunine coals, although the invention is not limited.

thereto, and the comminuted solid phase of the suspension will be referred to as sand.

In known apparatus of the type referred to, the bony coals, i; e. the middlings, are discharged by causing the current of suspension laden therewith to divert from its substantially horizontal path, either in upward or in downward direction. However, I have found that either method has certain drawbacks.

,If said current is caused to divert in upward direction, then, owing to the fact that its density increases in downward direction, suspension of its top layer, having a rela: tively low density, will be the first to be discharged and will naturally be supplemented by other suspensionfof the same layer and not, or only very partly, by suspension of the lower layers, whose densities are relatively high. That is to say, the discharge of suspension of the lower layers will lag behind that of suspension of the top layer, the consequence being that the discharge of the bony coals in the lower layers is retarded. Moreover, sand settling from the top layer will reach layers whose velocities of flow are lower than that of the top layer, so that the densities of said lower layers will increase. Stated with other :words: owing to the retarded discharge of the lower layers of suspension, the densities of these layers will increase. This will again reduce the velocities of flow of said layers and thereby still further increase the accumulation of bony coals therein, thus seriously interfering with the settling of the slate, i. e. the sinks.

:In case the direction of flow of the current of suspension' carrying the bony coals is caused to divert in downward direction with a viewto discharging said current from the receptacle, a similar phenomenon will occur. That is to say, the bottom layer of relatively high density will be the first to be discharged and the higher layers of lower density will lag behind. .Owing thereto, the settling of sand from said higher layers will gradually reduce the densities of said layers, whereby the discharge thereof will still further be interfered with.

The retardation of the dischar-ge of the middlings in the higher layers is a drawback especially in the wet cleaning of coals, since the amount of bony coals of relatively low specific agravity generally considerably exceeds the amount of bony coals of relatively high speciiic gravity, so that iby far the greater part of the middlings is carried by, the higher layers of the suspension. Besides, at the rear end of the tank theincrea'se, in downward direction, of the density of the suspension in the higher layers exceeds that in-the lower layers, and this phenomenon also favorably affects the accumulation of bony coals in said higher layers.

The main object of my present invention is to materially reduced the above disadvantages. With this object in view, I suggest that the top layer of the current of suspension carrying the middlings is discharged in horizontal or in upward direction, and that the lower layer of said current is discharged in downward direction. The result thereof is that the causes of the aforesaid progressive interference with the discharge of the middlings are for the greater part suppressed. As a matter of fact, any increase of thedensity of the lower part of the current dischargedin upward direction will be compensated for by a decrease of the density of the upper part of the our-.

" rent discharged in downward direction.

I shall nowproceed to describe my invention in further details with reference to the annexed diagrammatic drawing, in which Figures 1, 2 and 3 illustrate three diffcrent embodiments thereof. Fig. 1a showson an en'- larged scale a detail of the embodiment illustrated in Fig. 1, and Fig. 2a is a plan view of that portion of the, apparatus shown in Fig. 2 which issituated below-the plane A--A.

In the embodiment shown in Figs.'l and 1a, the tank has parallel, vertical side walls, a horizontal bottom 2, a downwardly sloping front wall 3, and a vertical rear wall 4 having an upwardly and rearwardly inclined weir 5. The lower part of the tank accommodates the horizontal portion of the lower part of an endless drag conveyor 6 driven in clockwise direction by suitable means not shown. The lower part of said conveyor sweeps the.

bottom and the front wall of the tank, and the. upper part thereof sweeps a false bottom 7 running in parallel relation with the front wall 3 and suitably spaced therefrom.

The lower part of a second conveyor 8, driven in counterclockwise direction by suitable means not shown, has a horizontal front portion sweeping the surface 9 of the suspension contained in the receptacle, the rear portion of said lower part sweeping an upwardly and rear-wardly inclined, perforated sheet 10, which has a width substantially equal to the inner width of the tank and whose lower portion 11 extends through a suitable distance below'the surface of the bath.

Provided some distance vertically above the surface of the bath and the false bottom 7, are pipes 12 for supplying relatively low density suspension to the tank, said pipes ibein-g perforated so as to evenly distribute said suspension through the full width of the bath. By means of curved guide sheets 13, said suspension is also evenly distributed through the full height of that portion of the bath which is situated above the conveyor '6.

- A horizontal, perforated pipe 14 for the supply of relatively heavy suspension to the space confined by the lower and the upper parts of the conveyor -6 is located above the surface 9 of the bath a small distance behind the upper edge of the front wall 3 of the tank.

The rear end of the bottom 2 is spaced some distance from the vertical rear wall 4, and opening from below into the slot so formed is a vertical conduit 15 connected,

through an elbow 16, with a riser provided with a weir 17 situated a substantial distance below the surface 9 manner wellknown in the art,

I The weir is pivoted as at 18 about a transverse horizontal axis and-is provided at its frontendwith a'curved', downwardly extending flange 19 permanently in contact with the top edge of the rear wall 4 so. as to prevent leakage of suspension in any'position'of the. Weir'S' within the range of 'adjustmentthereof, see Fig. 1a. The weir 5-supports an arm 36 hinged about atransverse. horizontal axis and secured to which is. a baflie plate 20 immersed in the top layer of'the bath.

A partition 21 is provided between the two parts of the conveyor 6' immediately in front of the rear roller about which said conveyor is passed';' Sai'dpartition' acts, in cooperationwith the scrapers ofthe. conveyor, as a sluice.

The numeral 22 designates a chute through which run-'of-mine'coalscan be fed. to the bath; and the un rneral 23 indicates a horizontal dewatering screen mounted with' its front end vertically below th'etop of," the conveyorifi and cooperating, with sprayers 23(1. .The front end of a second horizontal dewatering screen 24, cooperating with sprayers 2462, is disposed vertically below the weir 17.. g

' Thetop edge of the front wall "3' of the tankjis indi.-. cated by 25 and vertically below the same. isfthe rear end of a horizontal screen 26 cooperating with'fsprayers 26a. Mounted vertically below the front end of the. screen 2 4.is a boot 27 connected. at its bottom to. thesuction side of a pump 28 for feeding the pipe 14, andanother boot 29fserves to receive the overflow of boot 27. The bottom ofb'oot 29. is connected to the suction side; of. a pump 30 for feeding the pipes 12. i

The lower end of the vertical conduit 15 is connected, through a valve 31, to a compressed. air supplypipe not shown. i

The method of operating the apparatus described with reference to Figs. 1 and lais as follows. i

If runeof-min'e coals are supplied to the. bath in the therefrom by the upper part of the conveyor 6. so asv to.

fall-ontothe bottom 2 of the tank to be discharged by. the lower part of said conveyor.

The bony coals, i. e. the products whose specificgravities have values intermediate those ofthe pure. coals. and; of the slate, will be suspended in the suspensionabove. the upper part of the conveyor 6. Theyare carried; to

wards therear wall of. the tank both by said upper. part: of the conveyor 6; and by the suspension flowing towards; the rear wall 4 of the tank. The bony coals of relatively,

high specific gravity will, on reaching this wall, be. dis-1 charged, together with the suspension wherein they are; suspended, through the conduit 15, 16 andover. the. weirv 17, so as to fall'onto the dewateringv screen 24,.on the rear. portion of which they are washed by the water'from the sprayers. 24a and thus freed from the adhering sand.

That part. of the currentwhich carries the bony coals of. relatively low specific gravity is discharged by the weir 5. If this weirassumes its 'hghest position shown inFig. 1a, the baffle 20 assumes a position above the surface of the bath,'so that the surface layer of said current, i. e. the layer carrying the bony coals of'the lowestspec'ific gravity, will be discharged from the tank. In its:lowest position as illustrated in Fig. 1, the baflie- 20 forms. a bar.to the discharge of said' surface'layer,-so

that the next lower layer of: suspension'having a somewhat higher density is discharged together with the specifically somewhat heavier bony coals carried thereby;

The suspension overflowing the weir 5 and the bony coals carried thereby fall onto the screen 24 (but somewhat beyond the suspension discharged by way of the conduit. 15, 16) on which said coals are dewatered and washed by the water from the sprayers 24a.

The slate discharged from the tank, together with a certain amount of suspension, by the lower part of the drag conveyor 6 across the top edge 25 of the front wall 3, is received by the dewatering screen 26, the rear portion of which serves for removing the suspension. On the front portion of said screen, theslate is washed by water from the sprayers 26a so as to be freed from the adhering sand.

The relatively high densitysuspension discharged by the weir 17 is received by the boot 27 and is returned to the tank 1 by the pump 28 and the pipe 14. Thelevel of the weir 17 should be so adjusted that the amount'of suspension overflowing per unit of time exceeds'the capacity of the pump 28, so that-there will always be, a certain amount of overflow from the boot 27 into the boot 29, which receives the relatively low density suspension overflowing the weir-5. From the boot 29,'the suspension is returned to the tank 1 by means ofthe pump 30 and the pipes 12, which, distribute the suspen sion through the-full width and height of the bath above the level of the 'upper'part-of thedrag conveyor 6.

It' will be understood that in the apparatus just described with reference to Figs. 1 and in of the drawing by'far the greater part of the relatively high density. suspension supplied by the pipe 14 will flow below the false bottom 7and over the top edge of the partition 21 to'be discharged byway of the conduit 15, '16, only a verysmall part thereof being discharged, together with the slate, over the top edge 25 of the front wall 3.

"The bony coals of'relatively high specific gravity will float on. the surface of the current of the relatively high" density suspension. The scrapers of the drag conveyor 6" assist in carrying'said bony coals towards the conduit 15, 16, but since the specific gravity ofthese coals is lower than that of the relatively high density suspension, the flow of the suspension in. the conduit 15, 16 'may not be, strong enough to carry the entire amount of said coa1s,' and especially of the larger lumps thereof, towards the. weir 17. Consequently, it may be desirable for the suspension in the conduit 15 to be diluted with relatively low density suspension from the tank. With a view thereto, the amount of suspension discharged by the weir 17 per. unit of time may be allowed to exceed that supplied by. pipe .14, and this can be realized by permitting thesus pension in the boot 27 to overflow into the boot 29. The; amount of this overflowing suspension is practically equal, to the amount of relatively low'density suspension, which is: discharged, together with the, relatively highfdens'ity}. suspensionjthrough the conduit 15, 16., Since the boot. 27 functions as a thickener and provided it is suitably. dimensioned, it is possible forthe densities ofthes'us' pensions returned to the tank 1. by means of. the pumps. 28 and 30' to be kept substantially constant. Y

With a view to reducing the, density ofthe suspension: in the conduit '15 and immediately above the inlet thereof, i. e, at the rear of partition 21, airv may. be. blown into. said conduitby opening the valve 31. Since thefloating. purecoals are removedfromthe fluid'as at,11', it will.be,

appreciated that the disturbance createdby said air can;

nbt interfere with the purity of said. fioats,.and a similar.

remark applies tothe sinks (slate). I

Turning now to Figs. 2 and 2a, it will be seen that the vertical sidewalls of therear part of the tank 1, i; e. of,

the'part located vertically below the sheet 10 and=above the drag conveyor 6,'converge, andalso-that a wedge I member 36 is provided centrally betweenfsaidt cone verging side wall portions, said wedge member pointing IO'IlIGfi'OIIfi'WZIll of the tank. Owing to this construction,"

the velocity of flow of the fluid in the region of the weirs 5 and 17 is considerably increased, whereby the discharge of the bony coals, and especially those carried by the lower layers of the upper current of suspension, is favorably affected.

The sheet of the apparatus illustrated in Fig. 2 is imperforate, so that said sheet, cooperating with the scrapers of the drag conveyor 3, acts as a sluice for removing the top layer of the suspension in the tank 1 and discharging the same, together with the pure coals, onto the dewatering screen 23.

Owing to the fact that the submerged portions of the pure coals displace an equivalent volume of fluid, and assuming the level 9 of the bath to be constant, the amount of suspension discharged by the drag conveyor 3 will be variable and decrease as the amount of pure coals increases. This has the drawback that the amount of fluid overflowing the weir 5 will also vary. With a view to avoiding this drawback, it is suggested to measure the amount of fluid passing the screen 23 per unit of time and to increase the speed of the conveyor 8 if the measured amount is too small, and vice versa. To this end, the fluid passing the screen 23 may be collected in a receptacle 37 (see Fig. 2) having a bottom opening provided with a measuring disk 38. If now the level of the fluid in said receptacle and thereby the amount of fluid discharged per unit of time, is controlled by a float 39, the speed of the motor for driving the conveyor can be varied accordingly by apparatus well known in the art.

Fig. 3 illustrates an installation wherein the drag conveyor 6 shown in Figs. 1 and 2 is substituted by a boot 32 from which the slate may be removed in known manner by a bucket elevator not shown, or by a goose neck tube 33, in whose vertical portion the upward speed of flow should be relatively high. With a view thereto, said goose neck is provided with a compressed air inlet 34, so that it can function as an air lift, if so desired. The fluid thus raised, after passing the screen 26, is returned to the throat of the boot 32, the consequence being that the speed of flow in the gooseneck 33 may be increased at will whilst the fluid in the boot 32 remains practically stagnant. An installation of this type is suitable, for instance, for cleaning relatively small sized coals.

It will be appreciated that it is essential for the density of the suspension in the boot 32 to be uniform throughout the height thereof. In this respect, the fact that said boot is fed with relatively high density suspension is a favorable feature. Nevertheless, it may be desirable, in order to maintain the uniformity of the density, to provide for a downward flow of fluid in the boot 32, and this can be realized by drawing a certain amount of the suspension passing the dewatering screen 26 into the suction pipe of the pump 23 by opening a valve 35, which amount should be smaller, per unit of time, than the amount of relatively high density suspension supplied to the tank 1 by way of the pipe 14, so that a substantially horizontal flow of relatively high density suspension in the tank 1 vertically above the boot 32 and, as a consequence, overflow of said suspension into the conduit are ensured. This suspension is, as described hereinbefore, mixed with a suflicient amount of relatively low density suspension, in order to ensure that the bony coals floating thereon may settle in the conduit 15. The said amount of relatively low density suspension is practically equal to the amount of fluid overflowing boot 27 and can be controlled by vertically adjusting the weir 17.

By periodically operating the hinged baflle so as to check the surface current of suspension in thesame manner as described with reference to Fig. 1, the next lower, somewhat denser current of fluid together with the bony coals carried thereby is allowed to be discharged. In a similar manner, periodical operation of a hinged baflie 40 so as to set the same in a vertically upward position will periodically check the lower layer of the current of suspension of relatively high density, thereby causing the next higher, less dense fluid together with the bony coals suspended therein to be discharged from the tank.

Obviously, the means for removing the surface layer of suspension together with the pure coals floating thereon as illustrated in Fig. 2, i. e. the imperforate sheet 10,

coulde substitute the perforated sheet 10 shown in Figs. 1 and 3, and vice versa.

What I claim is:

l. A process for separating solid materials having different specific gravities by means of a suspension contained in a tank, consisting in creating substantially horizontal rectilinear currents in said suspension by supplying thereto suspensions of dilferent densities at diflerent heights at the front end of the tank, removing the floats and the sinks from the tank, hydraulically discharging the middlings by deflecting the upper part of the suspension with the middlings suspended therein in an upwardly inclined direction at the rear end of the tank and by deflecting the lower part of the suspension with the middlings suspended therein in downward direction at the rear end of the tank.

2. A process as claimed in claim 1, consisting in supplying a relatively low density suspension to the upper part of the tank, supplying a relatively high density suspension to the lower part of the tank, so that the amount of relatively high density suspension supplied to the lower part of the tank is smaller, per unit of time, than the total amount of suspension deflected in downward direction.

3. Apparatus for separating solids having different specific gravities, comprising a tank, means for supplying the solid materials having difierent specific gravities at the front end of the tank, means for supplying a suspension of relatively low and a suspension of relatively high density at an upper and at a lower level, respectively, of the tank at the front end thereof in a substantially horizontal direction and through substantially the full width thereof, means for discharging the suspension with middlings suspended therein from the tank both at a relatively high and at a relatively low level, an upwardly and rearwardly inclined plate having its front edge submerged below the normal level of the bath in the tank, mechanical means for removing floats from the bath across the said plate, means for removing sinks from the bath, and at least two weirs at different levels and at the rear end of the tank for discharging the suspension with middlings suspended therein, the lower weir communicating with a bottom opening of the tank by a U-shaped duct.

4. Apparatus in accordance with claim 3, wherein the upper weir is hinged about a horizontal axis transversely to the longitudinal axis of the tank, and is associated with means for imparting oscillatory movement thereto.

5. Apparatus in accordance with claim 3, wherein the rear end portion of the tank has rearwardly converging side walls.

References Cited in the file of this patent UNITED STATES PATENTS 2,139,047 Tromp Dec. 6, 1938 2,176,189 Rakowsky et al Oct. 17, 1939 2,458,035 Tromp Jan. 4, 1949 FOREIGN PATENTS 114,393 Australia Dec. 24, 1941 

